Mississauga occupies the southernmost portion of the region, and is, with 713,443 residents, the largest in population (the sixth-largest in Canada). It reaches from Lake Ontario north to near Highway 407. In the centre is Brampton, a city of 523,911 (ranked 9th by population in Canada). Finally, by far the largest in area and the most sparsely populated part of the region is Caledon, which is home to 59,460 residents.

The Region of Peel was created by the government of Bill Davis in 1974 from the former County of Peel, and was legislated to provide community services to the (then) rapidly urbanizing area of south Peel County (now Mississauga and Brampton).

In 2005, Peel Region approved without tender a $557 million waste management contract commitment lasting 20 years that can potentially allow it to dump garbage in Ontario landfill sites if Michigan bans Canadian trash.[5]

Seats on Peel Regional council are not assigned to member municipalities according to population or tax contributions, and this has produced considerable controversy within the region.[7]

Mississauga currently comprises about 62 per cent of the region's population and says it contributes 66 per cent of the taxes, but had been assigned 10 of the 21 council seats (or 48 per cent) distributed among the municipalities, with Brampton receiving six and Caledon five. In June 2005, the provincial government passed legislation[8] that will revise the composition of the council. Beginning in the 2006 municipal elections, one additional seat will be assigned to Brampton and two additional seats will be assigned to Mississauga, giving Mississauga 12 of the 24 seats assigned to municipalities.[9] These numbers do not include the regional chair, who is appointed by council members.

These changes are the result of a provincially appointed impartial arbitrator who noted:[10]

Regional councilors, whether or not they also wear an area (local) hat, represent all taxpayers in that region...no one area municipality has a majority of regional councillors. This is also why Mississauga's claim for two more regional representatives was seen as vexing - Mississauga would then have a majority at the regional level. Mississauga magnified the control issue by complaining of a historic underrepresentation given that a majority of taxpayers in Peel reside and have resided within Mississauga .. [I] recommend a continuation of a structure that denies any one area municipality a majority at the region.

— George W. Adams

Mississauga council, led by former mayor Hazel McCallion, has argued that Peel Region is an unnecessary layer of government which costs Mississauga residents millions of dollars a year to support services in Brampton and Caledon. Mississauga council unanimously passed a motion asking the Province of Ontario to separate Mississauga from Peel Region and become a single-tier municipality, arguing, among other things, the need to keep property tax dollars within the city of Mississauga for the good of the future of the City.[11]

Opponents of Mississauga's position, including former Brampton mayor Susan Fennell, have argued that from the 1970s through the 1990s, Mississauga was the chief beneficiary of Peel's infrastructure construction projects — funded by taxpayers in all three municipalities — and it is now Brampton's turn to benefit, as it is growing faster than Mississauga, which is mostly built-out.[12][13] As well, they have argued that common infrastructure, such as waste and water services, would be more efficiently managed at a regional level.

The region is responsible for the services and infrastructure related to water delivery and wastewater treatment, waste collection and disposal, some arterial roads, public health, long-term care centres, Peel Regional Police, Peel Regional Paramedic Services, planning, public housing, paratransit, judicial and social services. Other municipal functions are provided by the three local-tier municipalities. These responsibilities have changed over time, as functions have been uploaded and downloaded to and from the provincial and regional levels, as directed by the Province of Ontario.

Seven 400-Series Highways border or pass through Peel Region. These freeways are among the busiest and most modern of Ontario, mostly constructed since the 1970s, and have contributed significantly to the rapid growth of the Region. One of the welcome signs of Brampton has the slogan "All roads lead to Brampton" and shows six 400-series numbers (401, 403, 407, 409, 410, 427).